Method for applying a coating that acts as an electrolytic barrier and a cathodic corrosion prevention system

ABSTRACT

A coating system for ferrous and nonferrous metal substrates that provides cathodic protection from corrosion by coating with inherently conductive polymers and sacrificial anodic metal particles. The coating system is formed by a process that includes premixing of the inherently conductive polymer with the anodic metal particles to form an inherently conductive polymer/metal particle complex.

This application is a continuation application of U.S. Ser. No.10/205,048, filed Jul. 24, 2002, now U.S. Pat. No. 6,627,117 which is aContinuation-In-Part application of application Ser. No. 09/695,262,filed Oct. 24, 2000, now U.S. Pat. No. 6,440,332, which is aContinuation of application Ser. No. 09/361,505 filed Jul. 23, 1999, nowU.S. Pat. No. 6,231,789, which is a Continuation of application Ser. No.09/094,092 filed Jun. 9, 1998, now U.S. Pat. No. 5,976,419.

I. BACKGROUND OF THE INVENTION

A. Field of the Invention

This invention pertains to a corrosion prevention system and method ofproducing the same, and more specifically to a system for protecting ametal substrate from corrosion utilizing a cathodic coating comprisingat least one inherently conductive polymer and sacrificial metalparticles.

B. Description of the Related Art

One type of coating used to protect metals from corrosion is called abarrier coating. Barrier coatings function to separate the metal fromthe surrounding environment. Some examples of barrier coatings includepaints and nickel and chrome plating. However, as with all barriercoatings, holidays in the barrier coatings leave the metal substratesusceptible to corrosion. Electrochemically active barrier coatings,such as nickel, chrome, and conductive polymer, layers, call actuallyaccelerate corrosion of underlying metals at holidays in the coating.

Another type of coating used to protect metal substrates is calledsacrificial coatings. The metal substrate is coated with a material thatreacts with the environment and is consumed in preference to thesubstrate it protects. These coatings may be further subdivided intochemically reactive, e.g., chromate coatings, and electrochemicallyactive, or galvanically active, e.g., aluminum, cadmium, magnesium, andzinc. The galvanically active coatings must be conductive and are.commonly called cathodic protection.

In the art, a major difficulty has been the creation of a coating thatprotects like a cathodic system but is applied with the ease of atypical barrier coating system. Furthermore, there are manyenvironmental drawbacks with both traditional barrier and sacrificialmethods, from use of high levels of volatile organic compounds toexpensive treatment of waste waters produced by plating and subsequentsurface preparation for top-coating processes.

The present invention contemplates a new and improved coating system andmethod of producing the same which overcomes the foregoing difficultiesand others while providing better and more advantageous overall results.

II. SUMMARY OF THE INVENTION

In accordance with the present invention, a new and improved cathodiccorrosion resistant coating system is provided which may be easilyapplied in an environmentally friendly, efficient, safe and costeffective way to a metal substrate.

More particularly, the coating system utilizes at least one inherentlyconductive polymer in combination with galvanically anodic metalsdispersed in a resin matrix and applied to a metal substrate to create acathodic coating which is corrosion resistant.

According to one aspect of the invention, there is provided a method ofpreparing a coating system adapted for use on an associated metallicsubstrate, the coating system including a resin binder, an inherentlyconductive polymer, metallic particles which are anodic to the metallicsubstrate, and a curing agent. The method includes the steps of mixingthe inherently conductive polymer with the metallic particles to form ablend including an inherently conductive polymer/metal particle complex;providing a resin binder selected from the group consisting ofwater-borne resin systems and solvent-borne resin systems, providing acuring agent; and, mixing the blend, the resin binder, and the curingagent prior to application to the associated metallic substrate.

According to another aspect of the invention, the step of mixing theinherently conductive polymer with the metallic particles includes thesteps of mixing the inherently conductive polymer with metallicparticles at a process temperature of between 100° F. to 220° F.,inclusive.

According to another aspect of the invention the process temperature ismaintained for a sufficient period of time, in order to drive off apredetermined amount of H₂.

According to another aspect of the invention the step of mixing theblend, the resin binder and the curing agent includes the steps ofpreparing a Part A resin component by combining the blend with the resinbinder; preparing a Part B cure component including the curing agent;and, combining a predetermined amount of the Part A resin component witha predetermined amount of the Part B cure component immediately prior toapplication to the associated metallic substrate.

According to another aspect of the invention, the step of mixing theblend, the resin binder and the curing agent includes the steps ofpreparing a Part A resin component including the resin binder; preparinga Part B cure component by combining the blend with the curing agent;and, combining a predetermined amount of the Part A resin component witha predetermined amount of the Part B cure component immediately prior toapplication to the associated metallic substrate.

According to another aspect of the invention, the method furtherincludes the step of combining a predetermined amount of nano-scalepolymerized clay materials with the blend prior to the step of mixingthe blend, the resin binder, and the curing agent.

According to another aspect of the invention, the method furtherincludes the step of combining a predetermined amount of nano-scalepolymerized clay material into the resin binder prior to the step ofmixing the blend, the resin binder, and the curing agent.

According to another aspect of the invention, the step of mixing theinherently conductive polymer with the metallic particles furtherincludes the steps of providing the inherently conductive polymer in anamount from approximately 1% to 35% by volume of the coating system;and, providing the metallic particles in an amount from approximately 5%to 20% by volume of the coating system.

According to another aspect of the invention, there is provided acoating system formed by the method provided above wherein theinherently conductive polymer is at least one member of the groupconsisting of polyaniline, lignosulfonic acid-doped polyaniline,polypyrrole, polythiopene, polyacetylene, poly (p-phenylene), poly(p-phenylene vinylene), poly (p-phenylene sulfide) and polyanilinesubstituted with alkyl, aryl, hydroxy, alkoxy, chloro, bromo, or nitrogroups; the metal is at least one member of the group consisting ofaluminum, cadmium, magnesium, zinc, aluminum alloys, cadmium alloys,magnesium alloys and zinc alloys; the resin binder is at least onemember of tie group consisting of polyurethanes, epoxies, neutralresins, acidic resins, acrylates, polyesters, and glycidyl acrylates;and, the curing agent is at least one member of the group consisting ofsulfonamide, anhydride types, free radical photoinitiators, cationicphotoinitiators, and amine types.

According to another aspect of the invention, the at least oneinherently conductive polymer comprises between 1% and 35% by volume ofthe coating system.

According to another aspect of the invention, the metal comprisesbetween 5% and 20% by volume of said coating composition.

According to another aspect of the invention, there is provided a methodof protecting a metallic substrate from corrosion including the steps ofpreparing a coating system comprising a resin binder, an inherentlyconductive polymer, metallic particles which are anodic to the metallicsubstrate, and a curing agent wherein the inherently conductive polymeris premixed with the metallic particles at a predetermined processtemperature for a predetermined period of time to form a inherentlyconductive polymer/metal particle complex; preparing a surface of themetallic substrate for adhesion to the coating system; coating theprepared surface with the coating system; and, curing the coatingcomposition to form a corrosion resistant coating on the preparedsurface.

According to another aspect of the invention, the coating system is apowder coating system and the step of coating the prepared surface withthe coating system includes the step of electrostatically applying thecoating system to the associated substrate.

According to another aspect of the invention, there is a coating systemformed by the method provided above wherein the inherently conductivepolymer is substituted with an electroactive material and may be amember of the group consisting of tannins, o-catechol, p-catechol,1,4-phenylenediamine, 1,2-phenylenediamine, trimer of aniline (i.e.oxidative polymerization product of 1 mole of 1,4-phenylenediamine and 2moles of aniline) and several organic dyes.

According to another aspect of the invention, at least one electroactivematerial comprises between 1% and 35% by volume of the coating system.

One advantage of the present invention is that the claimed process canprovide water-borne or solvent-borne coating systems.

Another advantage of the present invention is that the claimed processproduces coating systems having improved performance in the areas ofcorrosion protection, adhesion, hardness, stability, etc. over similarformulations, having the same ratios of the components made in aconventional manner.

Another advantage of the present invention is that a powder coatingsystem utilizing the claimed process may be electrostatically applied.

Another advantage of the present invention is the cost effectiveness ofthe process. The coating may be produced at a reasonable cost andapplied with existing application systems. Use of the inventive coatingsystem will extend service life and reduce the costs associated withcorrosion maintenance.

Another advantage of the present invention is that the methods disclosedherein may be used in formulations over a wider pH range thanconventional coating systems.

Another advantage of the present invention is the provision of coatingcompositions utilizing the amine family of hardeners in conjunction withthe inherently conductive polymer without de-doping effects.

Still other benefits and advantages of the invention will becomeapparent to those skilled in the art to which it pertains upon a readingand understanding of the following detailed specification.

III. BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthis specification and illustrated in the accompanying drawings whichform a part hereof and wherein:

FIG. 1 shows a process flow chart for producing three types of cathodiccoatings according to the invention.

FIG. 2 shows a process flow chart for producing a coating systemaccording to the invention.

IV. DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention concerns a cathodic coating for ferrous ornon-ferrous metal substrates. Generally, the coating system utilizesinherently conductive polymers and metal particles anodic to themetallic substrate dispersed in a coating matrix. It has been found thatthe coating system disclosed herein provides unexpected andsignificantly improved corrosion protection by forming an adherent,electrochemically active, and truly cathodic protective coating.

The inventive coating system effectively creates an electron path by thethorough dispersion of one or more conductive polymers and metalparticles which eliminates dielectric barriers associated with otherorganic systems, thus creating a protective galvanic corrosion cell.

The present invention is directed to coating systems utilizing at leastone inherently conductive polymer and metal particles anodic to thesubstrate which are pre-blended in predetermined proportions beforedispersion in either the resin base, or the curing component. Thecoating systems of the present invention may be formulated as highsolids systems, radiation curable systems, and powder coat systems andmay be water borne or solvent borne.

For the purposes of the present invention, “High Solids” means anambient temperature curable coating that complies with the Los AngelesCounty Rule 66 definition, i.e. 80% non-volatiles by volume or greater.“Radiation Curable” involves the polymerization and cross-linking offunctional monomers and oligomers (usually liquid, can be a powder) intoa cross-linked polymer network (usually a solid film) induced by photons(UV curing) or electrons (EB curing). The curing can occur by eitherfree radical or cationic polymerization. Infrared and beta radiation canalso be utilized as energy sources for some radiation cure processes.“Powder Coating” involves coating objects with electrostaticallysprayed, thermally sprayed, or fluidized polymer powder under influenceof thermal energy causing the fine powder to melt or cross link aroundthe object and upon cooling to produce a compact polymeric layer. Theprocess steps and equipment to produce the coatings of the presentinvention are described below.

In general, the preferred conductive polymer for use in each of thesystems is polyaniline. Aluminum is the preferred anodic metalparticulate, however, any anodic metal that creates sufficient potentialdifference from the metal substrate may be used according to theinvention. Preferably, at least a 0.02 volt potential difference isestablished. In the preferred embodiment, the coating should produce apolarize cathode surface of −0.85 volts or more electronegativepotential when measured using a copper-copper sulfate electrode placeclose to the electrolyte/structure interface. This measurement isactually a measurement of voltage drop at the interface of the metallicsubstrate surface and the electrolyte with the reference cell being onecontact terminal and the metal surface being the other terminal.

General formulations for the coating systems according the invention areset forth as follows:

A. Resin Base:

-   -   1. High Solid Coatings        -   a. Polyurethane        -   b. Epoxy        -   c. Neutral or acidic pH resins    -   2. UV Radiation Curable        -   a. Acrylates        -   b. Polyurethane        -   c. Epoxy        -   d. Polyester    -   3. Powder Coat        -   a. Epoxy        -   b. Polyurethane        -   c. Polyester        -   d. Glycidyl acrylate        -   f. Hybrids or resin blends, i.e. polyester and epoxy            B. Inherently Conductive Polymers    -   1. Polyaniline    -   2. Polypyrrole    -   3. Polythiopene    -   4. Polyacetylene    -   5. Poly (p-phenylene)    -   6. Poly (p-phenylene vinylene)    -   7. Poly (p-phenylene sulfide)    -   8. Polyaniline substituted with alkyl, aryl, hydroxy, alkoxy,        chloro, bromo, or nitro groups        C. Anodic Metal Particles    -   1. Aluminum    -   2. Cadmium    -   3. Magnesium    -   4. Zinc    -   5. Alloys of the above metals        D. Plasticizers    -   1. Sulfonamide    -   2. Phosphate Ester types        E. Curing Agents    -   1. Sulfonamide    -   2. Anhydride types    -   3. Photoinitiators        -   a. free radical types        -   b. cationic types            F. Other Additives    -   1. Surfactants    -   2. Catalysts    -   3. Adhesion Promoters    -   4. Solvent        G. Electroactive Material    -   1. Tannin    -   2. o-catechol    -   3. p-catechol    -   4. 1,4-phenylenediamene    -   5. Trimer of aniline    -   6. Organic dyes.

With reference to FIG. 1, a process flow chart describing each type ofcoating system is provided. The following examples of each of thesystems show how the instant invention may be practiced, but should notbe construed as limiting the invention. The general process is describedwith exemplary materials in parentheses.

High Solids System

The process steps for making and applying an exemplary high solid systemare shown in FIG. 1, steps 1.a. through 1.g.

The process for making the coating is outlined in steps 1.a. through1.c. Any suitable multi-agitator mixer may be utilized for the blending,dispersion, and grinding operations.

The conductive polymer (polyaniline powder) is dispersed in a quantitysufficient to achieve the desired potential along with a plasticizer(sulfonamide) into a resin base (polyurethane). The dispersion is highshear mixed for approximately 30 to 45 minutes at a process temperatureof from approximately 70° to 150° F.

Any remaining additives and solvent (not to exceed about 15% by weight),are added to the dispersion and blended for additional time, whilemaintaining the process temperature. If a two-part coating system isdesired, the catalyst should not be added to this mixture until justprior to application of the coating.

The metal, in the form of finely divided particles (aluminum powder orflake), is added to the mixture in a quantity sufficient to achieve thedesired potential. Preferably, pure low oxidation aluminum flake oraluminum powder atomized and quenched in an inert environment is used.The aluminum can also be coated with stearic acid to preserve thedeoxidized surface. Disperse and grind this mixture further utilizingthe same equipment as the previous steps. Grind and disperse foradditional 45 minutes or until desired fineness of grind is achievedwhile maintaining the process temperature below 150° F.

Step 1.d. is a packaging step. Any suitable polypropylene or plasticcontainer can be utilized as packaging. The high solid coating mixturecan be discharged directly from the mixing vessel into the packagingcontainer. If a two part system is used, Parts A and B would be packagedseparately using methods known in the art.

Surface preparation of the substrate is outlined in step 1.e. A blastcabinet or similar means may be utilized for mechanical surfacepreparation. Alternately, other methods of surface preparation,including chemical means such as deoxidizing baths, may be utilized. Thepreferred method comprises lightly blasting the substrate with aluminumoxide grit. The prepared surface should be coated as soon as possible.

Step 1.f. outlines the application of the coating to the substrate. Thehigh solids system is suitable for various methods of applications thatare well known and practiced in the art. The coating should bethoroughly mixed prior to application by stirring or shaking. Also, thecatalyst should be added at this time if a two-part coating is used. Thecoating can be applied by dipping, brushing, rolling, or spraying.Coating should be applied uniformly to all surfaces to be coated to awet coat thickness sufficient to achieve a wet film thickness of 2 to 10mils.

Step 1.g. is a curing step. Curing can be accomplished by allowing thecoated item to stand 24 to 72 hours at room temperature to achieve cure.This process may be accelerated by curing in a thermal oven at 150° F.for 1 to 4 hours.

Radiation Curable System

The process steps for an exemplary radiation curable system are shown inFIG. 1, steps 2.a. through 2.g.

The process for making the coating is outlined in steps 1.a. through1.c. The conductive polymer (polyaniline) is dispersed in a quantitysufficient to achieve desired potential along with a plasticizer(sulfonamide) into the resin base (polyurethane). The dispersion isaccomplished by adding components to mixer, blender, attritor, ormulti-agitator mixer and high shear mixing for roughly 15 to 30 minutes,maintaining a process temperature of 100° to 140° F.

Any remaining monomers, oligomers, additives, and photoinitiators areadded to the polyaniline dispersion and low shear blended for anadditional 15 to 30 minutes while maintaining a process temperaturebelow 140° F.

The metal particles (aluminum flake or powder) are then added to themixture in a quantity sufficient to achieve desired potential.Preferably, pure low oxidation aluminum flake or aluminum powderatomized and quenched in an inert environment is used. The aluminum canalso be coated with stearic acid to preserve the deoxidized surface.Disperse and grind this mixture further utilizing the same equipment asin the previous steps. Grind and disperse an additional 30 to 45 minutesor until desired fineness of grind is achieved.

Step 2.d. is a packaging step. Because this coating system is UVcurable, the packaging container must be opaque. Any plastic orpolypropylene container that blocks ultraviolet light is suitable forpackaging this material.

Step 2.e. is the surface preparation step. Again, as with the highsolids system, any suitable means of preparing the substrate surface forcoating may be utilized.

Step 2.f. is the application of the coating to the prepared substrate.The coating should be thoroughly mixed prior to coating by stirring orshaking. The coating may be applied by means such as dipping, brushing,rolling, spraying, or others already known in the art. Preferably, thecoating is applied uniformly to all surfaces to a wet film thickness of2–8 mils, which will correspond to an equivalent dry film thickness.

Step 2.g. is a curing step. The coating may be cured by exposure toultraviolet light, beta radiation, electron beam, or in some instancesinfrared light. One source of UV radiation suitable for curing thesecoatings produces UV light in the 250 to 500 nanometer wavelengthranges, at a power of 300 watts/inch.

Powder Coat System

In FIG. 1, steps 3.a. through 3.i., the process steps required toproduce a cathodic powder coating according to the invention areoutlined.

Step 3.a. is a dry mixing operation that can be accomplished in ablender. The preferred method of mixing is utilizing a vertical blenderfor dry mixing powders. In this step, a premix is made of the powderedresin base, conductive polymer powder (polyaniline powder), plasticizer(sulfonamide), curing agents, additives, and metal particles (aluminumflake or powder). The conductive polymer and metal particles should beadded in a quantity consistent with desired electrical potential. Thisstep may be carried out utilizing high shear mixers or low shear mixers,such as ribbon cutters or tumble blenders. Mix for approximately 1 houror until thoroughly mixed. The mixing preferably occurs at ambienttemperatures. It is important that the process temperature does notexceed the cure temperature for the selected resin system.

Step 3.b. is a melt compounding and extruding process which ispreferably accomplished in a reciprocating extruder. Melt compoundingassures that all the additives, conductive polymer and metal particlesare thoroughly dispersed in the molten resin base. Single screwreciprocating extruders are suitable for accomplishing this step. In thecase of thermosetting coatings the temperature should be maintained20°–50° F. above the melting point of the resin, but kept below 400° F.to avoid deteriorating the polyaniline.

In step 3.c. the melt is subjected to a cooling and flatteningoperation. The extrudate is cooled and flattened into a sheet about0.005 inch thick by passing it through chilled nip rolls and cooled onan air or water cooling belt.

Step 3.d. is a primary grind operation preferably performed by a crusherat the end of a cooling line. The cooled, compounded sheet is quitefriable and readily broken into chips measuring about 0.003–0.005inches.

Step 3.e. is a fine grinding operation performed in a cryogenic mixingand grinding vessel. The cryogenic grinding serves three purposes. Itallows the processing of low cure temperature thermoset powders, itpromotes fracture of the aluminum, and it reduces oxidation of aluminumin the coating. The chips should be ground until a desired screen meshachieved. Typical mesh size is from +325 to −400.

Step 3.f. is a packaging step. Any suitable plastic bag or polypropylenecontainer that seals the powder from moisture is acceptable. The finelyground powder coating may be discharged directly from the grindingvessel into the packaging container.

Step 3.g. is the process of surface preparation of the substrate.Mechanical means, such as a blast cabinet may be utilized. Additionally,any suitable means for surface preparation may be utilized.

Step 3.h. is the coating application step. The powder coating accordingto the invention may be applied using an electrostatic spray system, orother application means known in the art. If the powder coating isapplied by thermal spraying, the substrate is usually preheated to atemperature slightly above the melting point of the powder.

Step 3.i. is the curing step. Cathodic thermoset powder coating systemsare typically cured in thermal ovens. Curing temperatures below 400° F.should be used to prevent deterioration of the polyaniline in thepowder. Cure is generally accomplished in 10 to 30 minutes. Cathodicthermoplastic powder coating systems that are thermally sprayed areallowed to cure utilizing residual heat produced by the thermal sprayand preheated substrate.

Typical formulations for the coating systems according to the presentinvention are presented below. The following examples are intended toshow various embodiments of the invention only and are not intended tolimit the scope of the invention. All of the volume percentages listedare considered approximate.

In the powder coating compositions, it has been found that advantagesare obtained when the ICP/Metal particle blend is encapsulated in adielectric binder. Such encapsulation enables electrostatic applicationmethods. The binder dissipates out when the coating is subjected to hightemperature curing, leaving behind the conductive pathway for electronflow.

EXAMPLE I High Solids System (Two Part)

COMPONENT TRADE NAME VOLUME % PART A Polyamide Resin Epon 828 50.00Polyaniline LIGNO-PANI 12.5  Aluminum Paste Eckart 235 37.5  100% Part APART B Amine Curing Agent Epicure-3192 90 Isopropyl Alcohol 10 100% PartB

Equal volume amounts of Parts A and B are mixed immediately prior toapplication to the substrate.

EXAMPLE II High Solids System (One Part)

COMPONENT TRADE NAME VOLUME % Urethane Resin 51.00 Phenolic Resin 5.00Polyaniline Powder Versicon 7.00 Aluminum Powder Al-120 12.00 Ethyltoluenesulfonamide Uniplex 108 5.00 VM & P naptha 3.00 Xylene 3.00Mineral Spirits 14.00

EXAMPLE IIA High Solids System (One Part) with Electroactive Materials

COMPONENT TRADE NAME VOLUME % Urethane Resin 51.00 Phenolic Resin 5.00Tannin Powder 7.00 Aluminum Powder Al-120 12.00 Ethyl toluenesulfonamideUniplex 108 5.00 VM & P naptha 3.00 Xylene 3.00 Mineral Spirits 14.00

The embodiment shown in IIA above is the formulation for the coatingsystem substituting electroactive materials for the inherentlyconductive polymer, wherein the electroactive material is a member ofthe group comprising tannins, o-catechol, p-catechol,1,4-phenylenediamine, 1,2-phenylenediamine, trimer of aniline (i.e.oxidative polymerization product of 1 mole of 1,4-phenylenediamine and 2moles of aniline) and several organic dyes. As an example, a reactionutilizing an electroactive material in conjunction with Aluminumparticles to prevent corrosion on an iron substrate is as follows:

Al → Al³⁺ + 3e⁻ E°_(anode) = E°_(A1)(OX) Ea(ox) → Ea(red) E°_(Ea) =E°_(Ea)(red) Fe³⁺ + 3e⁻ → Fe E°_(cathode) = E°_(Fe)(red) Overallreaction: Al + Fe³⁺ → E°_(cell) = E°_(anode) + E°_(Ea) + E°_(cathode)Al³⁺ + Fe

Therefore, the preferred (but not exclusive) reduction potential of theelectroactive species to be used in conjunction with an active speciesto protect a more noble one (i.e. substrate) is governed by thefollowing equation:E° _(Ea)≧−(E° _(anode) +E° _(cathode))

EXAMPLE III UV-Radiation Cure System

COMPONENT TRADE NAME VOLUME % Aliphatic urethane diacrylate Ebercryl4883 18.00 Isobornyl acrylate SR 506 33.00 Polyaniline powder Versicon10.00 Acrylate polyester oligomer Ebecryl 450 15.002-hydroxy-2-methyl-1-phenyl-1- Darocur 1173 5.00 propanoneHydroxycyclohexyl phenylketone Irgacure 184 0.50 Metallic diacrylate SR9016 5.00 Aluminum Powder AL-120 8.50 Ethyl toluenesulfonamide Uniplex108 5.00

EXAMPLE IV Powder Coat System

COMPONENT TRADE NAME VOLUME % Low density polyethylene NA204 71.5Polyaniline powder Versicon 16.00 Ethyl toluenesulfonamide Uniplex 1082.5 Aluminum Powder AL-120 10.00

The claimed improvements in corrosion resistance by use of the coatingsystems according to the invention are validated through markedlyimproved protection of the substrate when subjected to the salt spraytest. Coated panels were intentionally scribed and tested in accordancewith the procedure outlined in ASTM B117-95. The panels exhibited onlyslight surface oxidation at the damaged areas after 800+ hours in a saltspray chamber.

The ASTM B117 salt spray test utilized to test the corrosion resistanceof this cathodic coating system comprises a salt fog chamber. Thechamber is comprised of a fog chamber, salt solution reservoir,conditioned compressed air line, fog nozzle, specimen support racks,heater, and controller. The specimens are supported in racks at an anglebetween 15 and 30 degrees from vertical parallel to the principaldirection of horizontal flow of fog through the chamber. The saltsolution is mixed at 5% +/−1% salt by weight with water meeting therequirements of ASTM 1193-91, Type III. The pH of the condensed fog ismaintained between 6.5 and 7.2. Temperature in the chamber is maintainedat 95° F., +2° or −3°. Relative humidity in the chamber is maintained at95% to 98%.

The test specimens consist of standard 3×5 inch Q-panels, manufacturedfrom cold rolled 1010 steel. The panels are coated utilizing the methoddescribed. The substrate is then intentionally scribed to base metal inan “X” pattern. The partially exposed base metal allows evaluation ofthe cathodic properties of the coating versus its performance asstrictly an electrolytic barrier.

The test results indicate utilization of this coating method will extendthe service life of metals.

It has been discovered that improved performance and stability of thecoating composition employing an inherently conductive polymer (ICP), ametal, metal alloy or mixture thereof, and a resin binder system can beattained by utilizing certain processing techniques.

If the ICP is premixed with the metal particles, unexpected andadvantageous results occur. In the preferred method, illustrated in theflow chart of FIG. 2, the ICP is premixed with the metallic particles ata process temperature of at least 100° F., preferably 100° F. to 220°F., for a sufficient period of time, dependent on batch size, in orderto drive off H₂. At the upper end of the temperature range, thepreferred time period extends from ½ hour to 5 1/2 hours or more. Morepreferably, a longer induction time at the lower temperature range mayprove to be advantageous. For example, an induction time of 24 hours, ormore, in a hot house at the lower end of the temperature range providesthe desired results.

During the mixing process, the formation of hydrogen gas (H₂) occurs,such as would normally happen over a long period of time in a prior artfinished formulation, thereby resulting in instability of the coatingcomposition. However, it has been found that forcing the reaction duringthe production process assures a stable finished product. Applicant'salone have made this discovery, as no prior art teaches premixingmetallic particles with the ICP when preparing a coating system in orderto drive off H₂ and promote long-term stability of a coatingcomposition.

Applicants have further identified that processing the ICP with themetallic particles in the heating chamber removes unwanted oxidation ofthe metallic particles, presumably due to the acidic nature of the ICP.

In the premixing process, a blend is formed which contains the ICP,metallic particles, an ICP/metal particle complex, as well as a metaloxide. Formulations of coating systems employing this premix blend havedemonstrated increased corrosion performance, stability, and otherimproved qualities over similar formulations, having the same ratios ofthe components without the novel processing step.

Coating compositions utilizing the novel processing step retain thesought after cathodic/sacrificial properties, while providing improvedbarrier protection due to the inclusion of the metal oxide.

It has further been discovered that incorporation of “nano-scalepolymerized clay materials” (nanomers) into a preferred embodimentprovides improved barrier properties as well as improved electron flowfor the metal particles when combined with the ICP/metal particle blendand added to a coating system. By “nanomers” is meant composites ofmontmorillonite clays made up of Aluminum, Iron, and Magnesiumencapsulated in platelets of silica. These materials do exhibitconductive properties, thus enhancing electron flow of the metalparticles, and due to their complex molecular structures, they offerbarrier enhancement as well.

In addition, rheology agents which assist in flowability, hardness, anddispersion of the ICP/metal blend may be included in a preferredembodiment of a coating system according to the invention.

Further, applicants' invention is not limited to solvent-borne coatingsystems. Because water-soluble conductive polymers are available, thepresent invention may be provided with a water-borne resin binder.

In the prior art, it is well known to use “two-part” coating systemswherein Part A is generally the base resin and Part B is generally thecuring agent. It is common practice to provide epoxy resin formulationswherein the Epoxy base resin (Part A) is utilized with an Amine-typecuring agent (Part B). However, in the practice of tie prior art, it hasbeen impossible to utilize the inherently conductive polymers (ICP) withan Amine-type curing agent due to the “de-doping” effect caused by theairline-type agent which renders the ICP non-conductive.

However, it has been discovered by the Applicants that the novelprocessing step of providing a blend including an ICP/metal particlecomplex allows the use of Amine-type curing agents in a two-part coatingsystem. This discovery offers the advantage of providing a curingpossibility at ambient temperature. Further, it has been found that theblend may be incorporated into either the Part A resin component or thePart B cure component, or both, during formulation of a two-part coatingsystem. Those of skill in the art will readily appreciate that the blendcan be incorporated into any component of a multi-part formulation.

One further advantage provided by the novel processing step of providinga blend is in the area of powder coating. The novel processing stepallows the formulation of a coating system which utilizes an inherentlyconductive polymer which can be electrostatically applied to thesubstrate. The ICP/metal particle complex is effectively encapsulated inthe powder binder. For example, epoxy spheres bind the ICP/metalparticle complex and dissipates the electrical charge. Thereafter,during cure, the heat releases the ICP/metal particle complex to providea viable cathodic coating.

In the practice of the present invention, certain inherently conductivepolymers which are lignosulfonic acid-doped polyaniline (ligno-pani) maybe preferred because it is water dispersible and soluble in commonorganic solvents such as DMSO and THF. Ligno-pami may also be preferreddue to its increased processability as well as reduced cost. Studiesconducted with ligno-pani formulations suggest that the ligno-pani canretain redox capacity up to a pH between 8–10, which allows for theapplicability of ligno-pani even in basic environments.

Further examples of preferred embodiments of the present invention areas follows:

EXAMPLE V Water Borne Coating Composition

COMPONENT TRADE NAME WEIGHT % Vol. % ICP Bayton P ~14 ~17 Metal PowderEckart Aluminum 5025 ~26 ~25 Resin RO Primer 3781 ~54 ~50 Water — ~6 ~7

EXAMPLE VI Coating Composition

COMPONENT TRADE NAME WEIGHT % Vol. % ICP Bayton P ~12 ~15 MetalParticles Eckart Aluminum 5025 ~35 ~35 Resin RO 3781 Primer ~53 ~50

A preferred method in which a laboratory batch of a water borne coatingcomposition was prepared is given below.

75 grams of Aluminum Paste (Eckart 5025) was placed in a mixing vessel.While stirring, 25 grams of the Inherently conductive Polymer Baytron Pwas added to the Aluminum material to form the inventive ICP/metalblend. The blend was mixed for 1 hour and placed in a plastic containerwith the lid loosened to enable outgassing of Hydrogen.

The plastic container was placed in a heating chamber maintained at 120°F. for a period of twenty hours allowing for an induction processbetween the ICP and the Aluminum which creates a Hydrogen gas release.Thereafter, the blend was cooled to ambient temperature.

100 grams of a Water-Borne Acrylic Latex Primer (RO5281) was placed inthe mixing vessel. While stirring, 100 grams of the ICP/aluminum blendwas added to the primer and mixed for 1 hour.

The finished formulation sat at ambient temperature for 48 hoursallowing for a digestion period.

EXAMPLE VII

Solvent Borne Coating Composition

A preferred method in which a laboratory batch of a solvent bornecoating composition was prepared is given below.

75 grams of an Aluminum paste (Eckart 236) was placed in a niixingvessel. While stirring, 25 grams of an Inlherently conductive Polymer(GeoTech Ligno-Pani) was added to the Aluminum paste and mixed for 1hour. The blend was placed in a plastic bottle.

The plastic bottle containing the blend was placed in a heating chambermaintained at 120° F. for a period of twenty-four hours allowing for aninduction process between the ICP and the aluminum paste. Thereafter,the blend was cooled to ambient temperature.

Part A: 50 grams of an Epoxy resin (Shell Upon 828) was placed in amixing vessel. While stirring, 100 grams of the ICP/aluminum blend wasadded and mixed for 1 hour. The composition was allowed to digest for 48hours at ambient temperature.

Part B: 50 grams of an Amine curing agent (Shell epi-cure).

At the time of application, Part A was placed in a mixing vessel. Whilestirring, Part B was added to Part A. While stirring, 4 grams ofIsopropyl alcohol was added to the mixing vessel in order to reduceviscosity. The finished formulation was allowed to digest for 30 minutesbefore application.

In an alternate method of preparation, the ICP/Metal particle blend canbe added to the Amine curing agent (Part B) rather than incorporating itinto the Epoxy Resin (part A). As above, Part A and Part B are mixedtogether at the point of application.

The invention has been described with reference to preferred embodiment.Obviously, modifications and alterations will occur to others upon areading and understanding of this specification. It is intended toinclude all such modifications and alternations in so far as they comewithin the scope of the appended claims or the equivalence thereof.

1. A method of preparing an electrochemically active premix blend,comprising: mixing ingredients consisting essentially of inherentlyconductive polymer powder and metallic particles to form anelectrochemically active premix blend and driving off a predeterminedamount of hydrogen gas from the premix blend, wherein the metallicparticles are selected from the group consisting of aluminum, cadmium,magnesium, zinc, aluminum alloys, cadmium alloys, magnesium alloys, andzinc alloys, and combinations thereof.
 2. The method of claim 1, whereinthe inherently conductive polymer powder is at least one member of thegroup consisting of polyaniline, polypyrrole, polythiopene,polyacetylene, poly (p-phenylene), poly (p-phenylene vinylene), poly(p-phenylene sulfide), ligno-pani, and polyaniline substituted withalkyl, aryl, hydroxy, alkoxy, chloro, bromo, or nitro groups.
 3. Themethod of claim 1 wherein the step of mixing the inherently conductivepolymer powder with the metallic particles includes the step of mixingthe inherently conductive polymer powder with metallic particles at aprocess temperature of at least 100° F. to drive off the hydrogen gas.4. The method of claim 1 further comprising the step of adding apredetermined amount of nano-scale polymerized clay materials into theblend.
 5. The method of claim 2 further comprising the step of adding apredetermined amount of nano-scale polymerized clay materials into theblend.
 6. The method of claim 1, wherein the step of mixing inherentlyconductive polymer powder with metallic particles to form anelectrochemically active premix blend further results in metal oxide inthe electrochemically active premix blend.
 7. The method of claim 2,wherein the step of mixing inherently conductive polymer powder withmetallic particles to form an electrochemically active premix blendfurther results in metal oxide in the electrochem ically active premixblend.
 8. The method of claim 2, wherein the inherently conductivepolymer powder is polyaniline and the metallic particles arealuminum-containing particles.
 9. An electrochemically active premixblend, comprising: (a) inherently conductive polymer powder; (b)metallic particles; and (c) an inherently conductive polymer/metalparticle complex, wherein the metallic particles are selected from thegroup consisting of aluminum, cadmium, magnesium, zinc, aluminum alloys,cadmium alloys, magnesium alloys, and zinc alloys, and combinationsthereof, and wherein the conductive polymer powder, the metallicparticles, and the complex form an electrochemically active premix blendfor later mixing with a resin binder system to attain a coatingcomposition for cathodic protection.
 10. The blend of claim 9, whereinthe inherently conductive polymer powder is at least one member of thegroup consisting of polyaniline, polypyrrole, polythiopene,polyacetylene, poly (p-phenylene), poly (p-phenylene vinylene), poly(p-phenylene sulfide), ligno-pani, and polyaniline substituted withalkyl, aryl, hydroxy, alkoxy, chloro, bromo, or nitro groups.
 11. Theblend of claim 9, further comprising a predetermined amount ofnano-scale polymerized clay materials.
 12. The blend of claim 10,further comprising a predetermined amount of nano-scale polymerized claymaterials.
 13. The blend of claim 9, wherein the blend further comprises(d) a metal oxide.
 14. The blend of claim 10, wherein the blend furthercomprises (d) a metal oxide.
 15. The blend of claim 9, wherein theinherently conductive polymer powder is polyaniline and the metallicparticles are aluminum-containing particles.
 16. The blend of claim 9,wherein the inherently conductive polymer powder is polyaniline and themetallic particles are zinc-containing particles.